This invention relates to an optical light source unit for an endoscope used to observe and photograph the body cavity.
The endoscope is provided with a flexible pipe, small in diameter, which is inserted into the body cavity. When the top end of the flexible pipe reaches a portion of the body cavity to be examined, the portion is optically observed or photographed through the window provided at the top end of the flexible pipe by means of glass fibers incorporated in the flexible pipe. For this purpose, the endoscope requires an artificial optical light source for illuminating the body cavity.
In an optical light source unit for an endoscope of this type, for use in the above-described observing optical system, an illuminating light beam is directed to a portion of the body cavity to be examined through a bundle of optical fibers incorporated in the flexible pipe. That is, it is necessary to apply illuminating light of high intensity from the optical source to the bundle of optical fibers having a limited optical conductive area. Furthermore, it is necessary to minimize thermal damage to the body cavity which may be caused by the illumination. In order to meet these requirements, a xenon discharge tube is generally employed as the optical source thereof.
The discharge tube in the unit requires the application of a high voltage for starting its discharge. In applying this high voltage to start the ignition of the discharge tube, in the conventional unit, a high voltage is applied to the discharge tube by depressing the start button, and the start button is released after the operator has visually detected that the discharge tube has ignited.
According to this ignition starting operation, the start button must be continuously depressed until the ignition maintaining state is established, and accordingly the discharge tube and its circuit means are forcibly placed under severe conditions by application of the high voltage. When the ignition maintaining state has been established in the discharge tube, it is one of the causes tending to lower the durability of the discharge tube.
Also, it is vitally necessary in using the endoscope that a part of the optical source unit be inserted into the body cavity. Therefore, special care must be paid to the prevention of the leakage of high voltage of the optical source unit to the endoscope.
In photographing the body portion to be examined, high speed shutter control is required to obtain a clear image of the portion. For this purpose, it is necessary to provide illuminating light much higher in intensity than the above-described observing illuminating light. Moreover, in view of the aforementioned problem of thermal damage to the body cavity, the high brightness illumination for photographing the portion to be examined should be limited to a period of time as short as possible, or only to a period of time required for the photgraphing operation.
The requirements for the optical source unit made by taking the body cavity to be examined into consideration are as described above. Furthermore, the optical light source unit should meet certain functional requirements to satisfy variable photographing conditions according to various portions of the body cavity and the physical characteristics of the various portions. Accordingly, the optical source unit of this type must be capable of emitting light which is sufficient in intensity to permit the photographing operation at a high shutter speed and to meet variable photographing conditions over a wide range.
In a photographing operation under illumination effected by an optical light source unit capable of emitting high intensity light as described above, the time lag of the shutter operation which may occur in an ultra-high speed photographing operation, as in the case of a closeup, is an appreciable factor causing exposure error. Therefore, an effective optical source unit cannot be obtained without solving the problem of time lag.